Dielectric Logging: Principles, Applications, and Examples from the Brazilian Oilfields

Abstract

This work aims to present a review of dielectric logging, including physical principles, petrophysical evaluation, and applications. In addition, we will present a history of its use in Petrobras oilfields. The dielectric properties are generated by the charge alignment created by an excitation provided by an electric field. In this sense, polar characteristics of water molecules allow quantification of volume of water present in the reservoir, independently of salinity. Owing to the shallow depths of investigation, dielectric tools are useful in evaluating residual oil in high uncertainty salinity conditions, especially in mature fields, where uncertainties occur due to injection of water and/or steam. Although this logging tool has a long history of use in the petroleum industry, it was rarely used in Petrobras oilfields due to the high specificity, limitations of the technique, and/or high cost. Considering high frequencies used and proximity between electrodes, the tool provides very shallow measurements, which makes it impossible to evaluate the virgin zone in most reservoirs. Due to these characteristics, the tool was widely employed in low mobility hydrocarbon formations, where mud filtrate invasion tends to be smaller. The dielectric tool was used in Petrobras to evaluate reservoirs with very high viscosity and fresh water, in which it showed good results in the quantification of water saturation and hydrocarbon mobility. Additionally, the tool was used in Pre-salt in order to evaluate residual oil saturation to diminish the uncertain of microresistivity logs. Besides evaluating water saturation, many works have shown other applications for dielectric logging, such as to determine conductivity, salinity, wettability, Archie's "m" and "n" electric parameters, CEC, and evaluation of laminated reservoirs.

Detection Performance Analysis of Array Dielectric Dispersion Logging Based on Sensitivity Function

“…The Array Dielectric Logging Tool (ADT) from Schlumberger uses multi-frequency and multi-source spacing detection modes to measure formation information, overcoming the limitations of traditional dielectric logging’s shallow detection depth and insufficient measurement information [ 14 , 15 , 16 , 17 , 18 ]. The Array Dielectric Logging Tool has been successfully used in the evaluation of reservoirs with fresh water and heavy oils, and because of its high vertical resolution it has been used for the evaluation of laminated reservoirs [ 19 , 20 ]. With the development of unconventional oil and gas resources, the application of array multi-frequency dielectric logging tools in oil fields is growing, both at home and abroad.…”

Fast Computing Method and Response Characteristic Analysis for Array Dielectric Logging

“…Dielectric logging is a crucial tool for finding and developing unconventional oil and gas reservoirs such as tight oil and gas, heavy oil, and carbonate rock [3,7,8]. It works at a high frequency with a short source spacing, necessitates high instrument measurement accuracy, and is heavily influenced by ambient conditions.…”